Battery and electric bicycle

ABSTRACT

According to one embodiment, a battery includes: a first wire; a second wire; a third wire; a first resistor; a first switch; a second switch; a second resistor; a voltage measurer; and a controller that calculates a second resistance value of the third wire using a first voltage of a first battery when the first switch is turned on and the second switch is turned off, a second voltage of a second battery when the first switch is turned on and the second switch is turned off, a third voltage of the second battery when the first switch is turned off and the second switch is turned off, and a first resistance value of the first resistor.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from Japanese Patent Application No.2016-020900 filed on Feb. 5, 2016, the contents of which areincorporated herein by reference in their entirety.

FIELD

Embodiments described herein relate generally to a battery and anelectric bicycle.

BACKGROUND

A battery module has a configuration in which a plurality of secondarybatteries are serially connected.

A battery measures voltages of the secondary batteries of the batterymodule and adjusts the voltages or amounts of charge.

In order to adjust a voltage or an amount of charge of a secondarybattery, it is necessary to calculate a resistance value of a wireconnected to the secondary battery in advance.

Some conventional methods of calculating a resistance value of a wireuse voltages which are measured before and after a current flows in acircuit.

However, since a resistance value of an internal resistor of a batteryis too small and is thus ignored, the resistance value of the internalresistor is not considered when calculating the resistance value of thewire.

Accordingly, in the conventional methods of calculating a resistancevalue of a wire, it is not possible to calculate an accurate resistancevalue of a wire.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a configuration of a battery.

FIG. 2 is a diagram showing a process flow of a wire-resistancecalculator.

FIG. 3 is a diagram showing a relationship between time and voltage of asecondary battery cell.

FIG. 4 is a diagram showing a relationship between time and voltage of asecondary battery cell.

FIG. 5 is a diagram showing a battery including a temperature measurer.

FIG. 6 is a diagram showing an electric bicycle including the battery.

DETAILED DESCRIPTION

According to one embodiment, a battery includes: a first battery thatincludes a first positive electrode and a first negative electrode; asecond battery that includes a second positive electrode and a secondnegative electrode; a first wire that connects the first positiveelectrode and the second negative electrode; a second wire that connectsthe first negative electrode and the second positive electrode; a thirdwire that connects the first wire and the second wire; a first resistorthat is inserted into the second wire between a junction point of thesecond wire and the third wire and the first negative electrode; a firstswitch that is inserted into the second wire between the first resistorand the first negative electrode; a second switch that is inserted intothe second wire between the junction point and the second positiveelectrode; a second resistor that is inserted into the second wirebetween the second switch and the second positive electrode; a voltagemeasurer that measures a voltage between the first switch and the firstnegative electrode in the second wire, a voltage between the secondresistor and the second positive electrode in the second wire, and avoltage of the junction point; and a controller, wherein the controllercalculates a second resistance value of the third wire using a firstvoltage of the first battery when the first switch is turned on and thesecond switch is turned off, a second voltage of the second battery whenthe first switch is turned on and the second switch is turned off, athird voltage of the second battery when the first switch is turned offand the second switch is turned off, and a first resistance value of thefirst resistor.

Hereinafter, embodiments will be described with reference to theaccompanying drawings.

Like elements will be provided with like reference signs.

The drawings are schematic or conceptual, and a relationship between athickness and a width of each element, and sizes, specific coefficients,and the like of the elements cannot be said to be the same as theyactually are.

The same element may be drawn with different sizes or specificcoefficients in the drawings.

First Embodiment

FIG. 1 shows a configuration of a battery 10.

The battery 10 includes a secondary battery module 11, a voltagemeasurer 12, a power source 13, a current measurer 14, a cell balancingcircuit 15, a cell balance controller 16, a storage 5, and awire-resistance calculator 17.

The secondary battery module 11 includes n secondary battery cells 11-1,11-2, . . . , and 11-n which are connected in series.

The secondary battery cells 11-1, 11-2, . . . , and 11-n are secondarybatteries such as lithium ion batteries.

It is assumed that electromotive forces of the secondary battery cells11-1, 11-2, . . . , and 11-n are defined as E_(l), E₂, , and E_(n),respectively, and internal resistors of the secondary battery cells11-1, 11-2, . . . , and 11-n are defined as Ri₁, Ri₂, . . . , andRi_(n), respectively.

The power source 13 is connected to a plus-side terminal and aminus-side terminal of the secondary battery module 11.

When the power source 13 is connected to the secondary battery module11, the secondary battery module 11 is charged.

The power source 13 may be replaced with a load for use.

The load is a circuit or an element that consumes electric power.

When the load is connected to the secondary battery module 11, electricpower of the secondary battery module 11 is consumed.

A voltage measuring line Lv₀ is a wire that connects a junction point T₀and the voltage measurer 12.

A voltage measuring line Lv_(n+1) is a wire that connects a junctionpoint T_(n+1) and the voltage measurer 12.

A voltage measuring line Lv₀₁ connects a junction point T₀₁ and thevoltage measurer 12.

A voltage measuring line Lv₁₂ connects a junction point T₁₂ and thevoltage measurer 12.

A voltage measuring line Lv₂₃ connects a junction point T₂₃ and thevoltage measurer 12.

A voltage measuring line Lv_(n+1) connects a junction point T_(nn+1) andthe voltage measurer 12.

The voltage measurer 12 measures a voltage between the plus-sideterminal and the minus-side terminal of the secondary battery module 11.

The voltage measurer 12 measures a voltage between a positive electrodeterminal and a negative electrode terminal of each of the secondarybattery cells 11-1, 11-2, . . . , and 11-n.

A junction point S₀₁ of the voltage measuring line Lv₀₁ and a junctionpoint S₁₂ of the voltage measuring line Lv₁₂ are connected.

A switch SW₁ and a resistor R₁ are inserted between the junction pointS₀₁ of the voltage measuring line Lv₀₁ and the junction point S₁₂ of thevoltage measuring line Lv₁₂.

The junction point S₁₂ of the voltage measuring line Lv₁₂ and a junctionpoint S₂₃ of the voltage measuring line Lv₂₃ are connected.

A switch SW₂ and a resistor R₂ are inserted between the junction pointS₁₂ of the voltage measuring line Lv₁₂ and the junction point S₂₃ of thevoltage measuring line Lv₂₃.

A junction point S_(n−1n) of a voltage measuring line Lv_(n−1n) and ajunction point S_(nn+1) of the voltage measuring line Lv_(nn+1) areconnected.

A switch SW_(n) and a resistor R_(n) are inserted between the junctionpoint S_(n−1n) of the voltage measuring line Lv_(n−1n) and the junctionpoint S_(nn+1) of the voltage measuring line Lv_(nn+1).

The voltage measuring line Lv₀₁ between the junction point T₀₁ and thejunction point S₀₁ includes a wire resistor Rl₀₁.

The voltage measuring line Lv₁₂ between the junction point T₁₂ and thejunction point S₁₂ includes a wire resistor Rl₁₂.

The voltage measuring line Lv₂₃ between the junction point T₂₃ and thejunction point S₂₃ includes a wire resistor Rl₂₃.

The voltage measuring line Lv_(nn+1) between the junction point T_(nn+1)and the junction point S_(nn+1) includes a wire resistor Rl_(nn+1).

The current measurer 14 is serially connected to the secondary batterymodule 11.

The current measurer 14 measures a current flowing in the secondarybattery module 11.

The cell balance controller 16 controls switching of the switches SW₁,SW₂, . . . , and SW_(n).

For example, when the switch SW₁ is turned on, the secondary batterycell 11-1 is connected to the resistor R₁ and the secondary battery cell11-1 is in a discharging state.

The wire-resistance calculator 17 calculates a resistance value of eachof the wire resistors Rl₀₁, Rl₁₂, . . . , Rl_(n−1n), and Rl_(nn+1).

The storage 5 stores the voltage values of the secondary battery cells11-1, 11-2, . . . , and 11-n measured by the voltage measurer 12, thecurrent values measured by the current measurer 14, and the resistancevalues of the wire resistors Rl₀₁, Rl₁₂, . . . , and Rl_(n−1n), andRl_(nn+1) calculated by the wire-resistance calculator 17.

The cell balance controller 16 and the wire-resistance calculator 17 maybe controlled by one controller (one circuit).

The cell balancing circuit 15 is a part including the secondary batterymodule 11, the switches SW₁, SW₂, . . . , and SW_(n), and the resistorsR₁, R₂, . . . , and R_(n).

The cell balancing circuit 15 is a circuit that equalizes the voltagesof the secondary battery cells 11-1, 11-2, . . . , and 11-n with eachother.

The cell balancing circuit 15 is not particularly limited as long as itcan individually charge and discharge one or more secondary batterycells.

Here, arrangement of parts will be described with a focus on thesecondary battery cell (a first battery) 11-1 and the secondary batterycell (a second battery) 11-2 among the secondary battery cells 11-1,11-2, . . . , and 11-n.

The positive electrode (a first positive electrode) of the secondarybattery cell 11-1 and the negative electrode (a second negativeelectrode) of the secondary battery cell 11-2 are connected by a wire (afirst wire) 1.

The negative electrode (a first negative electrode) of the secondarybattery cell 11-1 and the positive electrode (a second positiveelectrode) of the secondary battery cell 11-2 are connected by a wire (asecond wire) 2.

A wire (a third wire) 3 connects the junction point T₁₂ of the wire 1and the junction point S₁₂ of the wire 2.

In the wire 2, the resistor (a first resistor) R₁ is inserted in seriesbetween the junction point S₁₂ and the negative electrode (the firstnegative electrode) of the secondary battery cell 11-1.

In the wire 2, the switch (a first switch) SW₁ is inserted in seriesbetween the resistor (the first resistor) R₁ and the negative electrode(the first negative electrode) of the secondary battery cell 11-1.

In the wire 2, the switch (a second switch) SW₂ is inserted in seriesbetween the junction point S₁₂ and the positive electrode (the secondpositive electrode) of the secondary battery cell 11-2.

In the wire 2, the resistor (a second resistor) R2 is inserted in seriesbetween the switch (the second switch) SW₂ and the positive electrode(the second positive electrode) of the secondary battery cell 11-2.

The voltage measurer 12 measures a voltage between the resistor R₂ andthe positive electrode (the second positive electrode) of the secondarybattery cell 11-2 in the wire 2, a voltage between the switch SW₁ andthe negative electrode (the first negative electrode) of the secondarybattery cell 11-1 in the wire 2, and a voltage of the junction pointS₁₂.

The voltages of the secondary battery cells 11-1, 11-2, . . . , and 11-nwhich are measured by the voltage measurer 12 are defined as v₁ (V), v₂(V), . . . , and v_(n) (V).

The voltage of the secondary battery module 11 that is measured by thevoltage measurer 12 is defined as v (V).

The voltage measuring line Lv₀ and the voltage measuring line Lv₀₁ maybe formed as a single wire.

The voltage measuring line Lv_(n+1) and the voltage measuring lineLv_(nn+1) may be formed as a single wire.

The wire-resistance calculator 17 calculates the resistance values ofthe wire resistors Rl₀₁, Rl₁₂, . . . , Rl_(n−1n), and Rl_(nn+1) when theabsolute value of the current measured by the current measurer 14 issufficiently small, that is, when the secondary battery module 11 isneither charged nor discharged.

One of the switches SW₁ to SW_(n) is turned on every predeterminedinterval k, and the resistance values of the wire resistors Rl₀₁, Rl₁₂,. . . , Rl_(n−1n), and Rl_(nn+1) are calculated.

Here, k is a predetermined natural number and is preferably 1 or 2.

When k=1, the cell balance controller 16 turns on the switch SW₁.

When the switch SW₁ is turned on, the wire-resistance calculator 17calculates the resistance values of the wire resistor Rl₀₁ and the wireresistor Rl₁₂.

The cell balance controller 16 turns off the switch SW₁ and then turnson the switch SW₂.

The wire-resistance calculator 17 calculates the resistance values ofthe wire resistor Rl₁₂ and the wire resistor Rl₂₃.

The resistance value of the wire resistor Rl₁₂ is calculated two timeswhen the switch SW₁ is turned on and when the switch SW₂ is turned off.

The wire-resistance calculator 17 can improve calculation accuracy ofthe resistance value of the wire resistor Rl₁₂ by calculating an averageof the resistance values of the wire resistor Rl₁₂.

When k=2, the cell balance controller 16 turns on the switch SW₁.

When the switch SW₁ is turned on, the wire-resistance calculator 17calculates the resistance values of the wire resistor Rl₀₁ and the wireresistor Rl₁₂.

The cell balance controller 16 turns off the switch SW₁ and then turnson the switch SW3.

The wire-resistance calculator 17 calculates the resistance values ofthe wire resistor Rl₂₃ and the wire resistor Rl₃₄.

When k=2, the wire-resistance calculator 17 calculates the resistancevalues of the wire resistors Rl₀₁, Rl₁₂, . . . , Rl_(n−1n), andRl_(nn+1) at least one time.

Since the number of switches SW₁, SW₂, . . . , and SW_(n) which arecontrolled by the cell balance controller 16 is smaller than that ofwhen k=1, a time in which the wire-resistance calculator 17 calculatesthe resistance values of the wire resistors Rl₀₁, Rl₁₂, . . . ,Rl_(n−1n), and Rl_(nn+1) is shorter.

When k>2, all of the resistance values of the wire resistors Rl₀₁, Rl₁₂,. . . , Rl_(n−1n), and Rl_(nn+1) cannot be calculated, and thus all ofthe resistance values of all of the wire resistors Rl₀₁, Rl₁₂, . . . ,Rl_(n−1n), and Rl_(nn+1) are calculated by interpolation.

For example, it is assumed that the resistance values of the wireresistors Rl₀₁, Rl₁₂, . . . , Rl_(n−1n), and Rl_(nn+1) are the same.

At this time, an average value of the resistance values of the wireresistors Rl₀₁, Rl₁₂, . . . , Rl_(n−1n), and Rl_(nn+1) which arecalculated by the wire-resistance calculator 17 is set as the resistancevalues of all the wire resistors Rl₀₁, Rl₁₂, . . . , Rl_(n−1n), andRl_(nn+1).

FIG. 2 shows a process flow of the wire-resistance calculator 17.

The wire-resistance calculator 17 starts a process flow (Step 101).

The cell balance controller 16 turns off all switches (Step 102).

Here, j denotes the number of the switches SW₁, SW₂, . . . , and SW_(n)controlled by the cell balance controller 16, and j is any one of 1, 2,. . . , and n.

When j=1 (Step 104), the wire-resistance calculator 17 stores thevoltage v of the secondary battery module 11, the voltage v₁ of thesecondary battery cell 11-1, and the voltage v₂ of the secondary batterycell 11-2 which are measured by the voltage measurer 12 in the storage5, and defines the voltages as V′, V₁′, and V₂′.

Since no current flows in the secondary battery module 11, the voltageV′ of the secondary battery module 11, the voltage V₁′ (a fifth voltage)of the secondary battery cell 11-1, and the voltage V₂′ (a thirdvoltage) of the secondary battery cell 11-2 are the same as anelectromotive force E₁+E₂+ . . . +E_(n) of the secondary battery module11, the electromotive force E₁ of the secondary battery cell 11-1, andthe electromotive force E₂ of the secondary battery cell 11-2,respectively, (Step 105).

When the cell balance controller 16 turns on the switch SW₁, a currentflows in the secondary battery cell 11-1, the wire resistor Rl₀₁, theresistor R₁, and the wire resistor Rl₁₂ (Step 106).

The voltage measurer 12 stores the measured voltage v of the secondarybattery module 11, the measured voltage v₁ of the secondary battery cell11-1, and the measured voltage v₂ of the secondary battery cell 11-2 inthe storage 5, and defines the voltages as the voltage V of thesecondary battery module 11, the voltage (a first voltage) V₁ of thesecondary battery cell 11-1, and the voltage (a second voltage) V₂ ofthe secondary battery cell 11-2 (Step 107).

The wire-resistance calculator 17 calculates the resistance value rl₀₁of the wire resistor Rl₀₁ and the resistance value (a second resistancevalue) rl₁₂ of the wire resistor Rl₁₂ using the voltage V′ of thesecondary battery module 11, the voltage V₁′ of the secondary batterycell 11-1, and the voltage V₂′ of the secondary battery cell 11-2 whichare measured by the voltage measurer 12 when the switch SW₁ is turnedoff in Step 105 and the voltage V of the secondary battery module 11,the voltage V₁ of the secondary battery cell 11-1, the voltage V₂ of thesecondary battery cell 11-2, and the resistance value (a firstresistance value) of the resistor R₁ which are measured by the voltagemeasurer 12 when the switch SW₁ is turned on in Step 107, and stores thecalculated resistance values in the storage 5 (Step 108).

The cell balance controller 16 turns off the switch SW₁ (Step 109).

It is checked whether j=n is established (Step 119).

When j=n is not established, j=j+k is set in Step 120 and it is checkedwhether j>n is established in Step 121.

When it is determined that j>n is not established in Step 121, theprocess flow is returned to Step 104.

When it is determined that j>n is established in Step 121, j=n is set inStep 122 and the process flow is returned to Step 104.

Here, a method of calculating the resistance value rl₀₁ of the wireresistor Rl₀₁ and the resistance value rl₁₂ of the wire resistor Rl₁₂ inStep 108 will be described below.

The voltage V of the secondary battery module 11, the voltage V₁ (thefirst voltage) of the secondary battery cell 11-1, and the voltage V₂ ofthe secondary battery cell 11-2 which are measured by the voltagemeasurer 12 when the switch SW₁ is turned on in Step 107 are expressedby Equation (1), Equation (2), and Equation (3).

Equation (1)

V=V′−(Ri ₁)×I ₁   (1)

Equation (2)

V ₁ =V ₁′−(Ri ₁ +Rl ₀₁ +Rl ₁₂)I ₁   (2)

Equation (3)

V ₂ =V ₂ ′+Rl ₁₂ ×I ₁   (3)

Here, when a current flowing in the resistor R₁ is defined as I₁, thecurrent I₁ can be calculated by Equation (4) using the voltage v₁ of thesecondary battery cell 11-1 and a known resistance value r₁ of theresistor R₁

$\begin{matrix}{{Equation}\mspace{14mu} (4)} & \; \\{I_{1} = \frac{V_{1}}{r_{1}}} & (4)\end{matrix}$

Accordingly, by substituting Equation (1), Equation (3), and Equation(4) into Equation (2) and arranging the equation with respect to thewire resistor Rl₀₁, the resistance value rl₀₁ of the wire resistor Rl₀₁can be calculated by Equation (5).

$\begin{matrix}{{Equation}\mspace{14mu} (5)} & \; \\{{rl}_{01} = {\left( {V_{1}^{\prime} - V_{1} + V^{\prime} - V + V_{2}^{\prime} - V_{2}} \right)\frac{r_{1}}{V_{1}}}} & (5)\end{matrix}$

By substituting Equation (4) into Equation (3), the resistance valuerl₁₂ of the wire resistor Rl₁₂ can be calculated by Equation (6).

$\begin{matrix}{{Equation}\mspace{14mu} (6)} & \; \\{{rl}_{12} = {\left( {V_{2} - V_{2}^{\prime}} \right)\frac{r_{1}}{V_{1}}}} & (6)\end{matrix}$

When j=1 is not established (Step 104) and j=n is established (Step110), the wire-resistance calculator 17 stores the voltage v of thesecondary battery module 11, a voltage v_(n−1) of a secondary batterycell 11-n−1, and the voltage v_(n) of the secondary battery cell 11-nwhich are measured by the voltage measurer 12 in the storage 5, anddefines the voltages as V′, V_(n−1)′, and V_(n)′.

Here, since no current flows in the secondary battery module 11, thevoltage V′ of the secondary battery module 11, the voltage V_(n−1)′ ofthe secondary battery cell 11-n−1, and the voltage V_(n)′ of thesecondary battery cell 11-n are the same as the electromotive forcesE₁+E₂+ . . . +E_(n), E_(n−1), and E_(n) of the batteries (Step 111).

When the cell balance controller 16 turns on the switch SW_(n), acurrent In (>0) flows in the secondary battery cell 11-n, the wireresistor Rl_(n−1n), the resistor R_(n), and the wire resistor Rl_(nn+1)(Step 112).

The voltage measurer 12 measures the voltage v of the secondary batterymodule 11, the voltage v_(n−1) of the secondary battery cell 11-n−1, andthe voltage v_(n) of the secondary battery cell 11-n, and defines themeasured voltages as V, V_(n−1), and V_(n) (Step 113).

The wire-resistance calculator 17 calculates the resistance valuesrl_(n−1n) and rl_(nn−1) of the wire resistors Rl_(n−1n) and Rl_(nn+1)using the voltages V′, V_(n−1)′, and V_(n)′ stored in the storage 5 bythe wire-resistance calculator 17 in Step 111 and the voltages V,V_(n−1), and V_(n) measured by the voltage measurer 12 in Step 113, andstores the calculated resistance values in the storage 5 (Step 114).

The cell balance controller 16 turns off the switch SW_(n) (Step 109).

It is checked whether j=n is established (Step 119).

Since j=n is established, the process flow moves to Step 123 and thenends.

The voltage v of the secondary battery module 11, the voltage V_(n) ofthe secondary battery cell 11-n−1, and the voltage V_(n−1) of thesecondary battery cell 11-n which are measured in Step 113 are expressedby Equation (7), Equation (8), and Equation (9).

Equation (7)

V=V′−(Ri _(n))×I _(n)   (7)

Equation (8)

V _(n−1) =V ₂ ′+rl _(n−1n) I _(n)   (8)

Equation (9)

V _(n) =V _(n)′−(Ri _(n) +rl _(n−1n) +rl _(nn+1))I _(n)   (9)

When j=1 is not established (Step 104) and j=n is not established (Step110), that is, when 1<j<n is established, the wire-resistance calculator17 stores a voltage v_(j−1) of a secondary battery cell 11-j−1, avoltage v_(j) of a secondary battery cell 11-j, and a voltage v_(j+1) ofa secondary battery cell 11-j+1 measured by the voltage measurer 12, anddefines these voltages as V_(j−1)′, V_(j)′, and V_(j+1)′.

Here, since no current flows in the secondary battery module 11,V_(j−1)′, V_(j)′, and V_(j+1)′ are the same as an electromotive forceE_(j−1) of the secondary battery cell 11-j−1, an electromotive forceE_(j) of the secondary battery cell 11-j, and an electromotive forceE_(j+1) of the secondary battery cell 11-j+1, respectively (Step 115).

The cell balance controller 16 turns on a switch SWj, and then a currentIj (>0) flows in the secondary battery cell 11-j, a wire resistorRl_(j−1j), a resistor R_(j), and a wire resistor Rl_(jj+1) (Step 116).

The voltage measurer 12 measures the voltage v_(j−1) of the secondarybattery cell 11-j−1, the voltage v_(j) of the secondary battery cell11-j, and the voltage v_(j+1) of the secondary battery cell 11-j+1 (Step117).

The wire-resistance calculator 17 calculates the resistance values ofthe wire resistor Rl_(j−1j) and the wire resistor Rl_(jj+1) using thevoltage V_(j−1)′ of the secondary battery cell 11-j−1, the voltageV_(j)′ of the secondary battery cell 11-j, and the voltage V_(j+1)′ ofthe secondary battery cell 11-j+1 stored by the wire-resistancecalculator 17 when all of the switches are turned off and the voltageV_(j−1) of the secondary battery cell 11-j−1, the voltage V_(j) of thesecondary battery cell 11-j, and the voltage V_(j+1) of the secondarybattery cell 11-j+1 which are measured by the voltage measurer 12 whenthe switch SWj is turned on (Step 118).

The cell balance controller 16 turns off the switch SWj (Step 109).

It is checked whether j=n is established (Step 119).

When j=n is not established, j=j+k is set in Step 120 and it is checkedwhether j>n is established in Step 121.

When it is determined that j>n is not established in Step 121, theprocess flow is returned to Step 104.

When it is determined that j>n is established in Step 121, j=n is set inStep 122 and the process flow is returned to Step 104.

A method of calculating the resistance values of the wire resistorRl_(j−1j) and the wire resistor Rl_(jj−1) in Step 118 will be describedbelow.

The voltage Vj−1 of the secondary battery cell 11-j−1, the voltage Vj ofthe secondary battery cell 11-j, and the voltage V_(j+1) of thesecondary battery cell 11-j+1 which are measured by the voltage measurer12 are expressed by Equation (10), Equation (11), and Equation (12).

Equation (10)

V _(j−1) =V _(j−1) ′+r _(j−1j) I _(j)   (10)

Equation (11)

V_(j)=r_(j)I_(j)   (11)

Equation (12)

V _(j+1)=(V _(j+1)′)+r _(jj+1) I _(j)   (12)

When a resistance value r_(j) of the resistor R_(j) is known, Equation(11) and Equation (12) are substituted into Equation (10) and resistancevalues r_(j−1j) and r_(jj+1) of the wire resistors Rl_(j−1j) andRl_(jj+1) are calculated by Equation (13) and Equation (14).

$\begin{matrix}{{Equation}\mspace{14mu} (13)} & \; \\{r_{j - {1j}} = {\left( {V_{j - 1} - V_{j - 1}^{\prime}} \right)\frac{r_{j}}{V_{j}}}} & (13) \\{{Equation}\mspace{14mu} (14)} & \; \\{r_{{jj} + 1} = {\left( {V_{j + 1} - V_{j + 1}^{\prime}} \right)\frac{r_{j}}{V_{j}}}} & (14)\end{matrix}$

A method of calculating the voltages of the secondary battery cells11-1, 11-2, . . . , and 11-n using the resistance values of the wireresistors Rl₀₁, Rl₁₂, . . . , Rl_(n−1n), and Rl_(nn+1) which aremeasured in FIG. 2 will be described below.

Under the control of the cell balance controller 16, all of the switchesSW₁, SW₂, . . . , and SW_(n) are turned off.

At this time, the voltages of the secondary battery cells 11-1, 11-2, .. . , and 11-n which are measured by the voltage measurer 12 are definedas V₁′, V₂′, . . . , and V_(n)′, respectively.

Under the control of the cell balance controller 16, operatingconditions of the switches SW₁, SW₂, . . . , and SW_(n) corresponding tothe secondary battery cells 11-1, 11-2, . . . , and 11-n are determined.

For example, when the voltage V₁′ (the fifth voltage) of the secondarybattery cell 11-1 is higher than a predetermined threshold voltage or ishigher than the voltages of other secondary battery cells such as thesecondary battery cell 11-2, it is determined that the switch SW₁corresponding to the secondary battery cell 11-1 should be turned on.

This determination is performed on the voltages V₁′, V₂′, . . . , andV_(n)′ of the secondary battery cells 11-1, 11-2, . . . , and 11-n.

That is, when it is determined that a secondary battery cell 11-m (wherem is any one of 1 to n) satisfies the operating condition, a switchSW_(m) corresponding to the secondary battery cell 11-m is turned on.

A cell voltage V_(m) of the secondary battery cell 11-m, in which theswitch SW_(m) is turned on, is detected by the voltage measurer 12.

The wire-resistance calculator 17 calculates a current I_(m) flowing ina resistor R_(m) from the cell voltage V_(m) when the switch SW_(m) isturned on.

That is, the wire-resistance calculator 17 calculates the current valueof the current I_(m) in the secondary battery cell 11-m, in which theswitch SW_(m) is turned on, on the basis of the resistance value of theresistor R_(m).

For example, when the switch SW₁ of the secondary battery cell 11-1 isturned on, the current value of the current I₁ is calculated on thebasis of the resistance value r₁ of the resistor R₁.

The current value of the current I₁ is calculated by “I₁=V₁/r₁.”

The wire-resistance calculator 17 calculates a voltage drop value ΔV_(m)which is generated in a wire resistor Rl_(m−1m) and a wire resistorRl_(mm+1) on the basis of the current value of the current I_(m).

The voltage drop value ΔV_(m) is calculated by“ΔV_(m)=I_(m)×(rl_(m−1m)+rl_(mm +1)).”

For example, when the switch SW₁ of the secondary battery cell 11-1 isturned on, the voltage drop value ΔV₁ which is generated by theresistance value rl₀₁ of the wire resistor Rl₀₁ and the resistance valuerl₁₂ of the wire resistor Rl₁₂ is calculated on the basis of the currentvalue of the current I₁.

The voltage drop value ΔV₁ is calculated by “ΔV₁=I₁×(rl₀₁+rl₁₂).”

The wire-resistance calculator 17 corrects the voltage V_(m) of thesecondary battery cell 11-m by adding the voltage drop value ΔV_(m) tothe voltage V_(m) of the secondary battery cell 11-m.

A true voltage of the secondary battery cell 11-m can be calculated by“V_(m)+ΔV_(m).”

For example, when the switch SW₁ of the secondary battery cell 11-1 isturned on, a true voltage (a fourth voltage) of the secondary batterycell 11-1 is calculated by adding the voltage drop value ΔV₁ to thevoltage V₁ of the secondary battery cell 11-1 detected by the voltagemeasurer 12 (V₁+ΔV₁).

j=1 is set in Step 103 and it is checked whether j=n is established inStep 119, but this checking may not necessarily be performed.

For example, when the resistance value of the wire resistor Rl₂₃ is setas j=2 in Step 103. it is checked whether j=2 is established in Step119.

Similarly, Step 103, Step 119, or the predetermined k may be changeddepending on the resistance value of the wire resistor Rl_(jj+1) whichwill be calculated.

Since resistors of wires between a certain secondary battery cell 11-xand junction points T_(x−1x) and T_(xx+1) can be considered as aninternal resistor Ri_(x) of the secondary battery cell 11-x, theresistor of the wire between the secondary battery cell 11-x and thejunction point T_(x−1x) and the resistor of the wire between thesecondary battery cell 11-x and the junction point T_(xx+1) do not haveto be considered.

Since a small current flows in the wires between the junction pointsS₀₁, S₁₂, . . . , and S_(nn+1) and the voltage measurer 12 for thepurpose of accurate voltage measurement, the wire resistors may beignored.

Step 105, Step 111, and Step 115 may be performed after Step 109.

FIG. 3 is a diagram showing the voltage v₁ of the secondary battery cell11-1 and the voltage v₂ of the secondary battery cell 11-2 which aremeasured by the voltage measurer 12 when the switch SW₁ is turned on oroff in the process flow shown in FIG. 2.

The horizontal axis represents time (seconds) and the vertical axisrepresents voltage (V).

A solid line indicates the voltage v₁ of the secondary battery cell 11-1and a broken line indicates the voltage v₂ of the secondary battery cell11-2.

Between a time t₁ and a time t₂, the switch SW₁ is turned on.

When the switch SW₁ is turned on, a current flows in the secondarybattery cell 11-1.

The voltage v₁ measured by the voltage measurer 12 at this time is notthe electromotive force of the secondary battery cell 11-1.

As expressed by Equation (2), the voltage of the secondary battery cell11-1, that is, the voltage between the junction point T₀₁ and thejunction point T₁₂, which should be measured cannot be measured due toan influence of a voltage drop in the wire resistors Rl₀₁ and Rl₁₂, inaddition to a voltage drop in the internal resistor Ri₁ of the secondarybattery cell 11-1.

Between the time t₁ and the time t₂, the voltage v₁ greatly decreases.

When the switch SW₁ is turned on, no current flows in the secondarybattery cell 11-2.

Since the voltage v₂ of the secondary battery cell 11-2 which ismeasured by the voltage measurer 12 is a voltage between the junctionpoint S₁₂ and the junction point S₂₃, a voltage rise due to the wireresistor Rl₁₂ is added thereto as expressed by Equation (3), and thevoltage increases to be more than it is before the time t₁ and after thetime t₂.

Accordingly, the voltage measurer 12 does not accurately measure thevoltage v₁ of the secondary battery cell 11-1 and the voltage v₂ of thesecondary battery cell 11-2.

FIG. 4 shows the voltage v₁ of the secondary battery cell 11-1 and thevoltage v₂ of the secondary battery cell 11-2 which are corrected usingthe resistance values of the wire resistors Rl₀₁, Rl₁₂, Rl_(n−1n), andRl_(nn+1) calculated by the wire-resistance calculator 17.

The horizontal axis represents time (seconds) and the vertical axisrepresents voltage (V).

A solid line indicates the voltage v₁ of the secondary battery cell 11-1and a broken line indicates the voltage v₂ of the secondary battery cell11-2.

Between a time t₁ and a time t₂, the switch SW₁ is turned on.

Immediately after the switch SW₁ is turned on, the voltage v₁ of thesecondary battery cell 11-1 drops due to the internal resistor Ri₁ ofthe battery.

This is because a voltage drop due to the wire resistor Rl₀₁ and thewire resistor Rl₁₂ is added to the voltage v₁ of the secondary batterycell 11-1 shown in FIG. 3.

Immediately after the switch SW₁ is turned on, the voltage v₂ of thesecondary battery cell 11-2 does not vary.

This is because a voltage rise due to the wire resistor Rl₁₂ issubtracted from the voltage v₂ of the secondary battery cell 11-2 inFIG. 3.

It is possible to accurately calculate the voltage v₁ of the secondarybattery cell 11-1 and the voltage v₂ of the secondary battery cell 11-2by correcting the voltage v₁ of the secondary battery cell 11-1 and thevoltage v₂ of the secondary battery cell 11-2 which are measured by thevoltage measurer 12 using the resistance values of the wire resistorsRl₀₁, Rl₁₂, . . . , Rl_(n−1n), and Rl_(nn+1).

The battery 10 is used for an electric bicycle 20 shown in FIG. 6.

Second Embodiment

FIG. 5 shows a configuration of the battery 10 including a temperaturemeasurer 18.

The battery 10 shown in FIG. 5 further includes the temperature measurer18 in addition to the components of the battery 10 shown in FIG. 1.

The same elements shown in FIG. 1 will be provided with the samereference signs, and a description thereof will not be repeated.

The temperature measurer 18 measures temperatures around the secondarybattery module 11 or the resistors R₁, R₂, . . . , and R_(n).

Since the resistance value r_(j) of the resistor R_(j) depends on thetemperature, the resistance value r_(j) varies depending on thetemperature.

A table in which the temperature measured by the temperature measurer 18and the resistance value r_(j) of the resistor R_(j) are correlated witheach other is stored in the storage 5 in advance.

A relationship between the temperature and the resistance value r_(j) ofthe resistor R_(j) is considered by setting temperature as thehorizontal axis and setting the resistance value r_(j) of the resistorR_(j) as the vertical axis.

When the temperature is defined as T, the relationship between thetemperature T and the resistance value r_(j) of the resistor R_(j) isexpressed by Equation (15).

Equation (15)

r _(j) =aT+b   (15)

Here, a denotes a slope and b denotes an intercept.

For example, a=0.04 and b=30 (Ω) are set.

For example, the wire-resistance calculator (a controller) 17 acquiresthe resistance value (a third resistance value) of the resistor R₁ (thefirst resistor) corresponding to the temperature measured by thetemperature measurer 18 from the table stored in the storage 5.

The wire-resistance calculator (the controller) 17 calculates theresistance value (a fourth resistance value) of the wire (the thirdwire) 3 using the voltage V₁ (the first voltage) of the secondarybattery cell 11-1 (the first battery), the voltage V₂ (the secondvoltage) of the secondary battery cell 11-2 (the second battery), thevoltage V′₂ (the third voltage) of the secondary battery cell 11-2 (thesecond battery), and the resistance value (the third resistance value)of the resistor R₁ (the first resistor).

The battery 10 including the temperature measurer 18 is used for theelectric bicycle 20 shown in FIG. 6.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A battery comprising: a first battery that comprises a first positive electrode and a first negative electrode; a second battery that comprises a second positive electrode and a second negative electrode; a first wire that connects the first positive electrode and the second negative electrode; a second wire that connects the first negative electrode and the second positive electrode; a third wire that connects the first wire and the second wire; a first resistor that is inserted into the second wire between a junction point of the second wire and the third wire and the first negative electrode; a first switch that is inserted into the second wire between the first resistor and the first negative electrode; a second switch that is inserted into the second wire between the junction point and the second positive electrode; a second resistor that is inserted into the second wire between the second switch and the second positive electrode; a voltage measurer that measures a voltage between the first switch and the first negative electrode in the second wire, a voltage between the second resistor and the second positive electrode in the second wire, and a voltage of the junction point; and a controller, wherein the controller calculates a second resistance value of the third wire using a first voltage of the first battery when the first switch is turned on and the second switch is turned off, a second voltage of the second battery when the first switch is turned on and the second switch is turned off, a third voltage of the second battery when the first switch is turned off and the second switch is turned off, and a first resistance value of the first resistor.
 2. The battery according to claim 1, wherein the controller calculates a fourth voltage of the first battery using the second resistance value of the third wire, the first voltage of the first battery, and the first resistance value of the first resistor.
 3. The battery according to claim 1, wherein when the first switch is turned off and the second switch is turned off, the controller turns on the first switch when a fifth voltage of the first battery is higher than the third voltage of the second battery, and turns on the second switch when the third voltage of the second battery is higher than the fifth voltage of the first battery.
 4. The battery according to claim 1, further comprising: a temperature measurer that measures a temperature around the first resistor; and a storage that stores a table in which the temperature and a third resistance value of the first resistor are correlated with each other, wherein the controller calculates the third resistance value corresponding to the temperature measured by the temperature measurer from the table stored in the storage, and calculates a fourth resistance value of the third wire using the first voltage of the first battery, the second voltage of the second battery, the third voltage of the second battery, and the third resistance value of the first resistor.
 5. An electric bicycle comprising the battery according to claim
 1. 